Various types of glow plugs are known and used; one such plug described in British Pat. No. 225,186 (to which German Pat. No. 406,932 corresponds), assigned to the assignee of this application, has an insulating body, for example a ceramic, about which a spiral heating wire is wound, the ceramic body protecting a central connecting bolt against attack by combustion gases. This type of glow plug has a high heat capacity and, due to the construction, requires a comparatively long preheating time. Thus, the time required for gas-fuel mixtures to reach the required ignition temperature is comparatively long. Construction of a glow plug of this type is comparatively difficult, so that the final price thereof is comparatively high.
It has also previously been proposed--see German Patent Disclosure Document No. 29 00 984, Sperner et al.--to utilize a tubular ceramic carrier for a heating spiral of a glow plug, in which the spiral can be in form of a wire, ribbon, or a layer applied to a carrier tube which is made of ceramic, quartz glass, glass ceramic, or high silicate glass. This type of glow plug, also, requires comparatively long preheat time.